Exam 2 Fall 2010
CHEM 4-1184 100 points
Name___KEY_________
Instructions: For multiple choice questions (2 pts each), circle the one appropriate answer A, B, C, etc. Show all
calculations for problems for credit. Write answers on the lines if they are provided. Draw a rectangle around
answers to problems.
1. One of the main features of Dalton's atomic theory no longer considered valid is: All atoms of each element are
identical in every respect. Which of the following is the best explanation of why this feature is no longer valid?
A. The existence of isotopes
B. Mass is conserved in a chemical change
C. Nearly all of the mass of an atom is concentrated in the nucleus
D. The total charge of the electrons of an atom exactly balances the positive charge of the nucleus
E. The planetary model of the atom has been shown to be incorrect
2. The nuclear symbol of an isotope of potassium is 41K
19
Indicate the number of protons, number of neutrons, atomic number, and mass number of the isotope.
Number of protons
Number of neutrons
Atomic number
Mass number
A.
19
22
19
41
B.
22
19
41
19
C.
19
41
19
22
D.
41
19
22
19
E.
41
19
41
22
3. Which of the following is a correct statement about the Rutherford alpha particle scattering experiment?
A. The experiment led to the conclusion that an atom consists of mostly open space.
B. The experiment established the fact that neutrons were one of the major subatomic particles.
C. The experiment showed why the planetary model of the atom is wrong.
D. The experiment provided evidence that electrons are found in the nucleus of an atom.
E. The experiment was controversial because it worked only with gold foils and no other metals.
4. A solute whose aqueous solution is a good conductor is called
A. a molecular substance
B. a cation
C. a strong electrolyte
D. a solvent
E. soluble
5. Which of the following is the best explanation of why a strong acid is an excellent conductor?
A. It is almost completely ionized in water.
B. It undergoes a vigorous chemical reaction with the water molecules.
C. It is soluble in water.
D. All acids are naturally excellent electrical conductors.
E. It reduces electronic vibration and thus allows greater conductivity.
6. Select the correct net ionic equation for the reaction that occurs, if any, when cesium metal (Z = 55) is placed in
hydrochloric acid. Cesium metal is above hydrogen gas in the activity series.
A. Cs(s) + H+(aq) → H(g) + Cs+(aq)
B. 2 Cs(s) + 2 H+(aq) → H2(g) + 2 Cs+(aq)
C. 2 Cs(s) + 2 H+(aq) + 2 Cl–(aq) → H2(g) + 2 Cs+(aq) + 2 Cl–(aq)
D. 2 Cs(s) + 2 HCl(aq) → H2(g) + 2 CsCl(aq)
E. There is no reaction
7. Calculate the mass percent of oxygen in Al2(SO4)3 (4 pts)
mass % O = mass 12 O-atoms x 100 = 12 x 16.00 g/mol x 100
= 56.11 %
mass total atoms
(2 x 26.98 + 3 x 32.07 + 12 x 16.00) g/mol
Name______ KEY___________
8. Fill in the blanks in the table below: (20 pts)
Give the IUPAC chemical name for the given
Compound
formula, or the formula for the given name
PCl5
phosphorous pentachloride
NH4OH (aq)
ammonium hydroxide or aqueous solution of ammonia
CBr4
carbon tetrabromide
H2S (g)
dihydrogen monosulfide
KMnO4
potassium permanganate
Al2(CO3)3
aluminum carbonate
silicon tetrafluoride
SiF4
lead (IV) sulfate
Pb(SO4)2
Ca(C2H3O2)2
calcium acetate
silver sulfide
Ag2S
silicon boride
Si3B4
CuCl
copper (I) chloride
mercuric phosphide
Hg3P2
lithium phosphate
Li3PO4
HBr (aq)
hydrobromic acid
HClO4 (aq)
perchloric acid
I2O4
diiodine tetraoxide
cobalt (II) acetate
Co(C2H3O2)2
chromium (III) sulfide
Cr2S3
HC2H3O2 (aq)
acetic acid
[Note: DO NOT CAPITALIZE CHEMICAL NAMES!]
Rule that applies
for naming
molecular compound
polyatomic ionic compound
molecular compound
molecular compound
polyatomic ionic compound
polyatomic ionic compound
molecular compound
polyatomic ionic compound + Stock
polyatomic ionic compound
ionic compound
ionic compound
ionic compound + Stock
ionic compound + Stock
polyatomic ionic compound
aqueous acid
aqueous acid
molecular compound
polyatomic ionic compound + Stock
ionic compound + Stock
aqueous acid
9. Nylon-6 is the most common form of nylon. The substance is composed of carbon, hydrogen, nitrogen and
oxygen. Determine the empirical formula of Nylon-6 if it contains the following mass percentages:
63.68% C, 9.80% H, 12.38% N, and the remainder is oxygen. (6 pts)
Based on 100%, %O = 100% - (63.68% + 9.80% + 12.38%) = 14.14%. Convert all percents to grams.
Divide mols of each atom by the lowest no. of mols, giving
mols C = 63.68 g C x 1 mol C/12.01 g C = 5.302;
5.302/0.8837 = 5.9998 = 6
mols H = 9.80 g H x 1 mol H/1.01 g H = 9.703 ;
9.703/0.8837 = 10.980 = 11
mols N = 12.38 g N x 1 mol N/14.01 g N= 0.8837;
0.8837/0.8837
= 1
mols O = 14.14 g O x 1 mol O/16.00 g O = 0.8838;
0.8838/0.8837
= 1
C6H11ON
10. A person who sweetens coffee with two teaspoons of table sugar (sucrose), C12H22O11, uses approximately 0.65
g. How many sugar molecules are in the teaspoon? (6 pts)
Adding the product of the number of C, H, and O atoms and their molar masses gives 342.34 g/mol as the molar
mass of sucrose.
molecules = 0.65 g sucrose x 1 mol sucrose x 6.022 x 1023 molecules sucrose = 5.7 x 1020
tsp
2 tsp
342.34 g sucrose
mol sucrose
Name_______ KEY __________
11. Calculate the number of formula units of nickel (II) sulfate in 457 g of this compound. (6 pts)
number of formula units NiSO4 = 457 g NiSO4 x 1 mol NiSO4 x 6.022 x 1023 formula units NiSO4
154.76 g NiSO4
1 mol NiSO4
= 1.78 x 1024
12. The empirical formula of a substance is NPCl2. Its molar mass is 347.64 g/mol. What is its molecular formula? (6
pts)
The empirical formula of NPCl2 weighs 115.88 g and the molecular formula must be a multiple (n) of this.
molar mass/empirical mass = 347.64 g/mol/115.88 g/mol = 3. So, the molecular formula is N3P3Cl6
13. Complete and balance the following reactions and name the kind of reaction on the lines at the right. If no
reaction occurs, indicate that by writing NR. (2 pts each)
Name of reaction
a.
2AgNO3 (aq) + H2S (g)
Ag2S (s) + 2HNO3 (aq)
double replacement
b.
2C3H8O (l)
c.
KHCO3 (aq)
d.
+
9O2 (g)
Δ
+ HCl (aq)
6 CO2 + 8 H2O
combustion_______
KCl (aq) + H2O (l) + CO2 (g)
metal carbonate decomposition
Rewrite the following English statement as a balanced equation on the line below and handle as
above:
Aqueous copper (II) nitrate reacts with aqueous sodium iodide to produce solid copper (I) iodide
plus aqueous iodine plus aqueous sodium nitrate.
Cu(NO3)2 (aq) + 4NaI (aq)
e.
Mn (s) +
2CuI (s) + I2 (aq) + 4NaNO3 (aq) oxidation-reduction
H2SO4 (aq)
MnSO4 (aq) + H2 (g)
single replacement
[Note: ok to use the common +2, +4, and +7 oxidation states for Mn]
f.
Sr (s) + H2O (l)
SrO (aq) + H2 (g)
Sr (s) + 2H2O (l)
Sr(OH)2 + H2 (g)
g.
Fe (s) + MgCl2 (aq)
h.
3NH3 (aq) + FeCl3 (aq) + 3H2O (l)
i.
barium acetate (aq) + sodium sulfate (aq)
NR
Ba(C2H3O2)2(aq) + Na2SO4 (aq)
j.
nitrogen (g)
+
or
single replacement
______________
Fe(OH)3 (s) + 3 NH4Cl (aq)
metal salt and
ammonia
double replacement
BaSO4 (s) + 2NaC2H3O2 (aq)
hydrogen (g)
+
3H2 (g)
2NH3 (g)
N2 (g)
[Note: recall the familiar combination reaction 2H2 + O2
combination
2H2O ]
Name______ KEY ________
14. Complete the table below by filling in all the empty cells. Make sure you write the appropriate chemical symbols
for the two missing atoms in the cells under 32
16 S . (7 pts)
Atomic
Notation
32
16
S
Number of
Neutrons
Atomic
Number
Number of
Protons
Number
of
Electrons
Atomic
Mass
16
16
16
16
32
207
82
Pb
125
82
82
207
207
59
28
Ni
31
28
28
28
59
15. Write a balanced chemical reaction to show the reaction of iron (III) chloride (aq) with fluorine gas to form
iron (III) fluoride (aq) and chlorine gas. (5 pts)
2 FeCl3 (aq) + 3 F2 (g) → 2 FeF3 (aq) + Cl2 (g)
16. Write the complete, total ionic, and net ionic equations that show what, if anything, happens when aqueous
solutions of hydrobromic acid and calcium hydroxide are mixed together. (5 pts)
Complete (molecular): 2 HBr (aq) + Ca(OH)2 → CaBr2 (aq) + 2 H2O (l)
Total ionic:
2 H+ (aq) + 2 Br- (aq) + Ca 2+(aq) + 2 OH- (aq) → 2 Br- (aq) + Ca 2+(aq) + 2 H2O (l)
Net ionic:
2 H+ (aq) + 2 OH- (aq) → 2 H2O (l)
Net ionic simplified:
H+ (aq) + OH- (aq) → H2O (l)
17. Define the word spontaneous using a complete English statement and give an example of spontaneity using a
chemical reaction that occurs spontaneously. (3 pts)
A chemical or physical process is spontaneous when it occurs by itself with no additional energy input. A
spontaneous process occurs to achieve a final state that is more stable than the initial state.
Water flowing down hill and acid-base chemical reactions such as HCl (aq) + NaOH (aq) → H2O (l) + NaCl (aq),
are examples of processes that occurs spontaneously.